This invention relates to a drum brake assembly, and more specifically, the invention relates to a drum brake assembly incorporating an electric parking brake actuator.
Vehicle brakes are used to slow the vehicle and also to maintain the vehicle in a parked position. Drum brakes are one common type of vehicle brake. Drum brake assemblies utilize opposing arcuate brake shoes that are movable away from one another into engagement with an inner surface of a drum to slow the vehicle. Typically, a hydraulic wheel cylinder forces the brake shoes into engagement with the drum. The same brake shoes may also be used to maintain the vehicle in the parked position. For example, drum brake assemblies have employed a separate mechanical linkage, or parking brake lever, that is actuatable by a cable to maintain the brake shoes in engagement with the drum. Such mechanical parking brakes have presented various problems that have been partially addressed by the use of electric parking brake mechanisms.
Some electric parking brake mechanisms have eliminated the parking brake lever and completely redesigned the drum brake assembly to incorporate the electric parking brake mechanism. These mechanisms have required high torque motors and a gearbox to generate sufficient force to apply the brakes, which adds significant cost to the drum brake assembly. Furthermore, high torque motors utilize a significant amount of power, which is undesirable in modern vehicles. Therefore, what is needed is an electric parking brake mechanism that requires relatively little power and that may be easily incorporated into a conventional drum brake assembly.
The present invention provides a drum brake assembly for a vehicle. The assembly includes a backing plate having primary and secondary support pins with primary and secondary brake shoes supported respectively thereon. Each of the brake shoes has a portion in spaced relation from one another. A drum is disposed about the brake shoes. A wheel cylinder is supported by the backing plate and is arranged between the portions of the brake shoes for forcing the portions away from one another to engage the brake shoes with the drum in a brake position. A strut interconnects the brake shoes proximate to the portions. A lever has a first end, which extends to a second end, supported from one of the portions by a pivotal connection. The lever is rotatable about the pivotal connection between a normal operating position in which the strut is spaced from the lever and a parking brake position in which the lever engages the strut to maintain the portions in the brake position. An electric parking brake actuator is supported by the backing plate and includes a linkage that coacts with the second end of the parking brake lever. The linkage is actuatable by the electric parking brake actuator for moving the lever between the normal operating and the park brake positions. The electric parking brake actuator moves the lever to the parking brake position in response to a parking brake signal with the brake shoes in the brake position.
Accordingly, the above invention provides an electric parking brake mechanism that requires relatively little power and that may be easily incorporated into a conventional drum brake assembly.